Previously, there is known a fuel injection device that includes a plurality of injection holes. The patent literature 1 discloses a structure, in which a diverging angle between a primary injection hole and a secondary injection hole, i.e., an injection-hole-to-injection-hole angle, which is an angle defined between central axes of the injection holes, is set to 15 to 25 degrees. With this setting, the Coanda effect is generated between fuel mists injected from the injection holes, so that the fuel mists are pulled toward each other. In this way, a rich mixture gas, which is atomized, is generated at a center side between the fuel mists.
It is assumed that an inner wall of each injection hole is shaped into a cylindrical form, i.e., a straight form at the fuel injection device of the patent literature 1. In the case where the inner wall of each injection hole is in the straight form, a large difference is generated between: a mist angle, which is an angle defined between outlines of the fuel mist injected from the injection hole at a time of generating a high fuel pressure in the fuel injection device; and a mist angle, which is an angle defined between outlines of the fuel mist injected from the injection hole at a time of generating a low fuel pressure in the fuel injection device. Therefore, a degree of the Coanda effect, which is generated between the fuel mists injected from the injection holes, may possibly be changed depending on the fuel pressure in the fuel injection device.
In the fuel injection device of the patent literature 1, in a case where the mist angle of the fuel mist injected from each injection hole is excessively increased at the time of, for example, the high fuel pressure, the Coanda effect may be excessively exerted, so that the fuel mists collide with each other to interfere the atomization of the fuel mist at the center side between the fuel mists. In contrast, in a case where the mist angle of the fuel mist injected from each injection hole is excessively reduced at the time of, for example, the low fuel pressure, the Coanda effect may not be exerted, so that the concentration of the mixture gas at the center side between the fuel mists may possibly be decreased.